As is known in the art, a frequency selective limiter (FSL) is a nonlinear passive device that attenuates radio frequency (RF) signals provided to an input thereof having a power level which is above a predetermined threshold power level. Hence, FSLs are said to limit the amount of power of an RF signal. RF Signals having a power level below the predetermined threshold power, on the other hand, propagate from the FSL input port to the FSL output port substantially unattenuated.
One feature of an FSL is the frequency selective nature of the high-power limiting. Specifically, an FSL has a characteristic such that low power signals (i.e. signals having a power level below the threshold power lever) close in frequency to the limited signals are substantially unaffected (i.e., the FSL does not substantially attenuate such signals).
A typical implementation of an FSL includes a stripline transmission structure provided from two layers of dielectric material disposed about a strip conductor, with the strip conductor having a fixed length and a fixed width along the length of the FSL. Such structures are relatively simple to fabricate and provide adequate magnetic fields to realize a critical power level of approximately 0 dBm when using a single crystal material. One method of reducing the threshold power level is to use a lower-impedance stripline at the cost of degraded return loss. An external matching structure can be used to improve the impedance match, but this technique reduces the bandwidth and increases the insertion loss of the FSL.